The present invention relates generally to clothes washing machines, and, more specifically, to a transmission therein.
In a typical machine for washing clothes, a vertical agitator is oscillated in two rotary directions during a wash cycle for washing clothes, and is driven in a single rotary direction during a spin cycle for removing water from the clothes by centrifugal force. The washer includes a transmission having an input shaft driven by an electrical motor, and an output shaft to which the agitator is mounted. The transmission typically includes a four-bar linkage or mechanism which converts unidirectional rotary motion to bi-directional oscillatory motion during the wash cycle. The mechanism includes a crank joined to the input shaft, with the crank being in turn joined to a connecting rod which in turn is connected to a follower link which is joined to the output shaft. The input and output shafts are suitably mounted in bearings and spaced apart from each other so that rotation of the crank in circles effects oscillatory movement of the follower am over a predetermined arc which determines the angular amplitude of agitator stroke in each cycle.
To obtain acceptable washing performance in the washer, the agitator must be oscillated at suitable stroke rate or angular velocity and with a suitable stroke arc or angular amplitude. The agitator must be driven with suitable torque and power to overcome the resistance due to the clothes and water in the washer which undergo agitation by the agitator during the wash cycle. Accordingly, the motor which drives the transmission must be correspondingly sized in output torque and power for meeting the demands of effectively washing the clothes.
Analysis of a typical four-bar transmission indicates that although the stroke amplitude effects an oscillatory cycle, the stroke motion diverges from a pure sine waveform. Since the stroke rate, or velocity, and acceleration are time derivatives of the stroke amplitude, they in turn diverge from corresponding sine waveforms. It can be shown that any divergence from a pure sine waveform increases the peak torque on the agitator shaft. The torque for oscillating the agitator is supplied by the motor through the transmission. Accordingly, the larger torques due to the non-sinusoidal stroke motion requires a suitably large drive motor for driving the agitator.